![Geological Survey of Canada Geological Survey of Canada](/web/20061103010152im_/http://www.gsc.nrcan.gc.ca/esst_images/gsc_e.jpeg) Natural Resources Canada > Earth Sciences Sector > Geological Survey of Canada > Past lives: Chronicles of Canadian Paleontology
Past lives: Chronicles of Canadian Paleontology Favosites polyps from Anticosti Island
Sometimes new insights in paleontology come from new ideas about
known fossils; other times it comes from the discovery of extraordinarily
preserved specimens such as Archaeopteryx, Aysheaia and, now, Favosites
![The tabulate coral Favosites from the Lower Silurian Jupiter Formation of Anticosti Island. The preserved soft polyps have been calcified and show 12-fold symmetry. Specimen is 12 cm across. (Photo by BDEC (c).) The tabulate coral Favosites from the Lower Silurian Jupiter Formation of Anticosti Island. The preserved soft polyps have been calcified and show 12-fold symmetry. Specimen is 12 cm across. (Photo by BDEC (c).)](/web/20061103010152im_/http://www.gsc.nrcan.gc.ca/paleochron/images/favos3_1.jpg) The tabulate coral Favosites from the Lower Silurian Jupiter Formation of Anticosti Island. The preserved soft polyps have been calcified and show 12-fold symmetry. Specimen is 12 cm across.
(Photo by BDEC (c).) |
The discovery in 1970 of a new subclass Sclerospongia in living reefs
in the Pacific and Caribbean was naturally of considerable interest to
marine biologists and reef ecologists. Paleontologists, however, were even
more excited about this discovery because these coralline sponges seemed
to be dead ringers for stromatoporoids -- those problematic calcareous
organisms that were the major builder of the great reef tracts of the
middle Paleozoic. Detailed work showed that they are indeed close kin. So,
previously taxonomic orphans, stromatoporoids have finally found a home in
this new subclass of the phylum Porifera.
Stromatoporoids are not the only fossil group thought to be allied with
the living sclerosponges. The Tabulata, extinct since the Paleozoic, were
simple colonial organisms that secreted a calcite skeleton composed
essentially of small tubes with horizontal partitions. The walls of the
tubes, which may be in contact, are commonly perforated. The Tabulata have
long been considered to be a group of colonial corals, although they are
quite different from the extinct rugose corals and the living hexacorals.
But some paleontologists have suggested that the Tabulata is another group
of Sclerospongia. All living corals and sea anemones possess
tentacle-bearing polyps, but because polyp tissue is soft and watery and
devoid of means for calcification, it has never been found fossilized.
That is, until a few years ago when Paul Copper of Laurentian University
in Sudbury discovered a few extraordinarily preserved specimens of the
tabulate Favosites in the Jupiter Formation (Early Silurian, 435
Ma) of Anticosti Island in the Gulf of St. Lawrence. These specimens
solved the question of the nature and identity of Tabulata because they
contain polyps. These Favosites colonies consist of little domes
5-6 cm across; the upper surface displaying crowded, prismatic
'corallites', each about 2 mm in diameter. Virtually every
'corallite' contains polyps preserved as calcite. The polyp is not
much more than a millimetre across, but each is seen to include a ring of
tentacles inwardly coiled in a retracted position. Each ring of tentacles
numbers 12.
![Closeup of coral Favosites calyces to show polyps. Field of view is about 1 cm across. (Photo by BDEC (c)) Closeup of coral Favosites calyces to show polyps. Field of view is about 1 cm across. (Photo by BDEC (c))](/web/20061103010152im_/http://www.gsc.nrcan.gc.ca/paleochron/images/favo2.jpg) Closeup of coral Favosites calyces to show polyps. Field of view is about 1 cm across.
(Photo by BDEC (c)) |
Because all corals possess polyps, and sponges do not, the
uniquely-preserved polyp-bearing specimens from Anticosti Island
demonstrate unequivocally that Favosites and probably all Tabulata
are corals. They further imply that Tabulata, with their twelve tentacles
stand apart from the tetracorals, hexacorals and octocorals (perhaps they
should be called 'dodecacorals').
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